As is generally known, a portable electronic product such as a notebook computer, a PDA, a portable DVD, a camcorder, a digital camera, and a mobile phone needs appropriate DC power supplied thereto in order to charge its battery or operate itself.
The DC power is supplied from a power supply. The power supply for supplying the DC power is generally classified into two types: an AC/DC power converter which converts the AC power supplied from a house or an office building into the DC power having predetermined voltage and current levels required to operate an electronic product; and a DC/DC power converter which converts the DC power supplied from airplanes, vehicles, vessels, or the like into the DC power, which is appropriate to operate the electronic product.
However, such a power supply was inconvenient for a user, who travels a lot, to use, because he or she must carry the two kinds of power converters both.
In order to avoid the problem, it has been proposed a power supply, which is able to receive AC and DC powers both. However, the power supply is just composed of two kinds of circuits coupled to each other, which perform different functions. Therefore, even when only one type of power is used, the power supply is structured to include a component element (hereinafter, referred to as “element”) for converting the other type of power therein as well. Therefore, the power supply is enlarged in size, and as a result, it is substantially impossible to carry along. Furthermore, the power supply requires a relatively large amount of power, which results in failing to realize an economic power consumption.
A typical switching mode power supply (SMPS) is a device which converts the input power supplied thereto to the power suitable for an electronic product regardless of the types of AC and DC input power, by changing the arrangement of an input condenser, a PWM control IC, a transformer or an inductor, a MOSFET switch, a diode, and an output condenser. Therefore, in the case of manufacturing a power supply for AC/DC and DC/DC conversion, which is able to receive AC and DC input power both, the power supply is provided with an element which can be commonly used for AC/DC conversion and DC/DC conversion, thereby realizing an effective power supply for AC/DC and DC/DC conversion. In the following, a conventional power supply will be described in reference to attached drawings.
FIG. 1A shows a circuit diagram of a conventional power supply, FIG. 1B is a circuit diagram of a conventional insulated DC/DC power supply, and FIG. 1C is a circuit diagram of a conventional non-insulated Boost-Up DC/DC power supply.
Referring to FIGS. 1A through 1C, each of the power supplies commonly employs an input condenser (C1 or C2), a PWM control IC (IC1 or IC2), a transformer (TL) or an inductor (L), a MOSFET switch (Q1 or Q2), a diode (D3) and an output condenser (C3).
Therefore, a key to the solution in manufacturing a power supply being capable of carrying out AC/DC and DC/DC conversion in one apparatus (referred to as “power supply for AC/DC and DC/DC conversion”) is to arrange elements, which are commonly usable for AC/DC conversion and DC/DC conversion both, inside the power supply, in order to provide a more efficient and more compact apparatus.
For example, an AC/DC power supply and an insulated DC/DC power supply can be installed together in order to manufacture the power supply for AC/DC and DC/DC conversion, but the structure causes a problem, in which a transformer is not easy to manufacture due to the difference between AC input voltage (100 to 230 VAC) and DC input voltage (12 to 16 VDC), even though it is advantageous in that the secondary sides of the two power supplies are completely common.
In order to solve the above problem, U.S. Pat. No. 6,134,125 discloses a power supply for AC/DC and DC/DC conversion, which is configured to include an AC input and a DC input individually, and structured to use an auxiliary transformer upon the DC input.
However, in the case of an electronic product such as a notebook computer requiring a high power, the insulated DC/DC power supply has defects of being enlarged in size and deteriorating the efficiency in comparison with the non-insulated DC/DC power supply, and therefore, the insulated DC/DC power supply cannot be effectively used in the power supply for AC/DC and DC/DC conversion requiring a high power.
Further, U.S. Pat. No. 6,459,604 issued to the applicant of the present invention discloses a universal power supply for AC/DC and DC/DC conversion which adopts a non-insulated DC/DC power supply suitable to the electronic products requiring a high power. Further, the universal power supply has an AC/DC converter and a DC/DC converter detachably connected with each other, thereby providing easy portability, and a predetermined voltage can be selected in a DC/DC mode.
However, the U.S. Pat. No. 6,459,604 could provide a highly efficient power supply in the case of a DC input, but in the case of an AC input, the universal power supply is degraded in efficiency and increased in size since the AC input passes through two converter circuits, that is, AC/DC converter circuit and DC/DC converter circuit.
Recently, U.S. Pat. No. 6,650,560 discloses a universal power supply for AC/DC and DC/DC conversion adopting a non-insulated DC/DC power supply, which is applicable to the electronic products requiring a high power and uses a feedback portion having a programmable resistor as a common portion.
Although the U.S. Pat. No. 6,650,560 provides a dual input AC and DC power supply capable of changing an output voltage by using a feedback portion having a programmable resistor as a common portion, the dual input power supply is large in size because it cannot provide a structure of reducing its size, for example, such that commonly usable elements, such as a transformer and an inductor, are installed integrally in one unit, thereby failing to realize miniaturization of the power supply.